JP7704634B2 - Method for grinding a workpiece - Google Patents

Description

The present invention relates to a method for grinding a workpiece that is applied when grinding a plate-shaped workpiece such as a wafer.

In order to realize small and lightweight device chips, there are increasing opportunities to thin wafers that have integrated circuits and other devices on their front side. For example, the front side of the wafer is held by a chuck table, and the chuck table and a grinding wheel with a grinding stone (grinding stone) containing abrasive grains fixed to it are rotated relative to each other, and the grinding stone is pressed against the back side of the wafer while a liquid such as pure water is supplied, thereby grinding the wafer to make it thinner.

However, when the entire wafer is thinned using the above-mentioned method, the rigidity of the wafer is significantly reduced, making it difficult to handle the wafer in later processes. Therefore, a technique has been proposed in which the central (inner) area of the wafer where the devices are provided is ground, and the outer edge (outer) area is left as is without being ground, thereby maintaining a sufficient rigidity of the wafer after grinding (see, for example, Patent Document 1).

In this technique, a grinding wheel with a fixed grindstone containing abrasive grains of a certain size is first used to roughly grind the central area of the wafer, forming a disk-shaped thin plate portion and an annular thick plate portion surrounding the thin plate portion on the wafer. In this way, by using a grinding wheel with a fixed grindstone containing large abrasive grains, the time required to grind the wafer can be shortened compared to using a grinding wheel with a fixed grindstone containing relatively small abrasive grains.

On the other hand, when a wafer is ground using a grinding wheel with a fixed grinding stone containing large abrasive grains, a damage layer containing scratches and distortions caused by the grinding is generated on the ground surface, and the mechanical strength (flexural strength) of the thin plate portion is likely to be insufficient. Therefore, after the wafer is roughly ground, the thin plate portion is further ground using a grinding wheel with a fixed grinding stone containing relatively small abrasive grains to remove the damage layer.

JP 2009-176896 A

When grinding the thin plate portion to remove the damaged layer, if the grinding wheel comes into contact with the side of the thick plate portion, the thick plate portion may be chipped. Therefore, when removing the damaged layer, only the central area of the thin plate portion is ground so that the grinding wheel does not come into contact with the thick plate portion. However, with this method, the damaged layer remains in the outer edge area of the thin plate portion (the area close to the boundary with the thick plate portion). As a result, during subsequent transportation, cracks extend from the remaining damaged layer to the front side of the wafer, making the device prone to damage.

By making the thin plate thicker and increasing the distance from the device on the surface side to the damaged layer sufficiently, it is possible to prevent damage to the device caused by cracks extending from the damaged layer. However, in this case, in order to thin the thin plate to its final thickness, a large portion of the wafer must be removed using a grinding wheel equipped with fixed grindstones that contain relatively small abrasive grains and can only remove a small amount per unit time. This means that the time required to complete grinding is significantly longer.

The object of the present invention is to provide a method for grinding a workpiece that can reduce the probability of damaging a device when grinding a plate-shaped workpiece having a device on its front side from its back side without significantly increasing the time it takes to complete grinding.

According to one aspect of the present invention, a method for grinding a workpiece, in which a plate-shaped workpiece having a plurality of devices provided on its front side is ground from its back side opposite to the front side using a grinding wheel attached to a rotating spindle, includes a step of attaching a protective member to the front side of the workpiece, a step of holding the workpiece via the protective member on a first holding surface of a first chuck table, and a step of setting the distance between the first holding surface and a first grinding wheel equipped with a first grinding stone containing abrasive grains, the first chuck table being closer to the first chuck than to a central side closer to the rotation axis of the first chuck table. a first grinding step in which, while rotating the first grinding wheel and the first chuck table, the first grinding wheel and the first chuck table are relatively moved in a direction intersecting the first holding surface to grind the workpiece from the back surface side, thereby forming a disk-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion on the workpiece; and after the first grinding step, the workpiece is held on a second holding surface of a second chuck table via a member, and a difference between a distance between a second grinding wheel provided with a second grinding wheel containing smaller abrasive grains than the first grinding wheel and the second holding surface at a center side close to the rotation axis of the second chuck table and a distance between an outer edge side far from the rotation axis of the second chuck table is smaller than a difference between a distance between the first grinding wheel and the first holding surface at a center side close to the rotation axis of the first chuck table and a distance between an outer edge side far from the rotation axis of the first chuck table and a second grinding step in which, while rotating the second grinding wheel and the second chuck table, the second grinding wheel and the second chuck table are moved relatively in a direction intersecting the second holding surface to grind the first thin plate portion from the back surface side, thereby forming a second thin plate portion that is disk-shaped and has a smaller diameter than the first thin plate portion and a second thick plate portion that is annular and surrounds the second thin plate portion on the first thin plate portion.

Preferably, the first chuck table is used as the second chuck table. Also, preferably, in the first grinding step, the first thin plate portion is formed to a thickness such that cracks extending from a damage layer including scratches or distortions generated on the outer edge side of the first thin plate portion in the first grinding step do not reach the device.

In one aspect of the present invention, a method for grinding a workpiece includes: adjusting the angle between the rotation axis of the first grinding wheel and the rotation axis of the first chuck table so that the distance between the first grinding wheel, which is provided with a first grinding stone containing abrasive grains, and the first holding surface of the first chuck table is wider on the outer edge side far from the rotation axis of the first chuck table than on the central side close to the rotation axis of the first chuck table; and forming a first thin plate portion having a disk shape and a first thick plate portion having an annular shape surrounding the first thin plate portion on the workpiece; therefore, the outer edge side of the first thin plate portion is thicker than the central side.

Then, the angle between the rotation axis of the second grinding wheel and the rotation axis of the second chuck table is adjusted so that the difference between the distance between the second grinding wheel, which is provided with a second grinding wheel containing smaller abrasive grains than the first grinding wheel, and the second holding surface of the second chuck table, at the center side close to the rotation axis of the second chuck table, and the distance between the second grinding wheel and the first holding surface at the center side close to the rotation axis of the first chuck table, and the distance between the first grinding wheel and the first holding surface at the outer edge side far from the rotation axis of the first chuck table, is smaller than the difference between the distance between the first grinding wheel and the first holding surface at the center side close to the rotation axis of the first chuck table, and the distance between the first grinding wheel and the first holding surface at the outer edge side far from the rotation axis of the first chuck table. In this state, the first thin plate portion is ground to form a second thin plate portion that is disc-shaped and has a smaller diameter than the first thin plate portion, and a second thick plate portion that is annular and surrounds the second thin plate portion. This makes it possible to form a second thin plate portion that has a smaller difference in thickness between the outer edge side and the center side than the first thin plate portion, while removing a damaged layer including scratches or distortion formed in the first thin plate portion.

In addition, in the method for grinding a workpiece according to one aspect of the present invention, the outer edge side of the first thin plate portion that remains on the workpiece as the second thick plate portion is thicker than the center side of the first thin plate portion, and the distance from the damage layer formed on the second thick plate portion (i.e., the outer edge side of the first thin plate portion) to the surface of the workpiece is sufficiently large, so that there is a low possibility that cracks will extend from the damage layer of the second thick plate portion to the surface side of the workpiece during subsequent transportation, etc., causing damage to the device.

Furthermore, in the method for grinding a workpiece according to one aspect of the present invention, a first thin plate portion is formed that is thinner at the center than at the outer edge, so the volume of the workpiece removed by the second grinding wheel is smaller than when the first thin plate portion, which is thick overall, is processed into a second thin plate portion. Therefore, even if the distance from the device to the damaged layer of the second thick plate portion (the outer edge side of the first thin plate portion) is made sufficiently large, the time until grinding is completed is not significantly extended. In this way, according to the method for grinding a workpiece according to one aspect of the present invention, the probability of device damage can be reduced without significantly extending the time until grinding is completed.

FIG. 1 is a perspective view showing a schematic view of a protective member being attached to a plate-shaped workpiece. FIG. 2 is a cross-sectional view that shows a schematic view of a state in which a workpiece is held on a chuck table via a protective member. FIG. 3 is a cross-sectional view that illustrates a process of grinding a workpiece by the first grinding wheel. FIG. 4 is a cross-sectional view showing a schematic view of a portion of the workpiece after it has been ground by the first grinding wheel. FIG. 5 is a cross-sectional view that typically shows how the first thin plate portion of the workpiece is ground by the second grinding wheel. FIG. 6 is a cross-sectional view that illustrates a portion of the workpiece after the first thin plate portion has been ground by the second grinding wheel.

Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. In the grinding method of the workpiece according to this embodiment, first, a protective member is attached to the plate-shaped workpiece to be ground (attaching step). Figure 1 is a perspective view showing a state in which a protective member 21 is attached to a plate-shaped workpiece 11.

The workpiece 11 is typically a disk-shaped wafer made of a semiconductor such as silicon (Si). The front surface 11a of the workpiece 11 is partitioned into a number of small regions by a number of mutually intersecting planned division lines (streets) 13, and a device 15 such as an IC (Integrated Circuit) is formed in each small region. In this embodiment, a portion of the workpiece 11 corresponding to the region (device region) in which the device 15 is formed is ground from the back surface 11b side opposite the front surface 11a to thin a portion of the workpiece 11.

In this embodiment, the workpiece 11 is a disk-shaped wafer made of a semiconductor such as silicon, but there are no limitations on the material, shape, structure, size, etc. of the workpiece 11. For example, a substrate made of other materials such as semiconductors, ceramics, resins, metals, etc. can also be used as the workpiece 11. Similarly, there are no limitations on the type, number, shape, structure, size, arrangement, etc. of the devices 15.

The protective member 21 attached to the workpiece 11 is typically a circular tape (film) having a diameter roughly equal to that of the workpiece 11, a resin substrate, a wafer of the same or different type as the workpiece 11, etc. An adhesive layer (not shown) that exhibits adhesive strength to the workpiece 11 is provided on the surface 21a side of this protective member 21.

Therefore, the protective member 21 can be attached to the workpiece 11 by bringing the surface 21a side of the protective member 21 into close contact with the workpiece 11. In this embodiment, as shown in FIG. 1, the protective member 21 is attached to the surface 11a of the workpiece 11 by bringing the surface 21a side of the protective member 21 into close contact with the surface 11a of the workpiece 11. This reduces the impact applied to the surface 11a when the workpiece 11 is ground from the back surface 11b side, thereby protecting the device 15 and the like.

After the protective member 21 is attached to the front surface 11a of the workpiece 11, the workpiece 11 is held by the holding surface of the chuck table via the protective member 21 (holding step). In other words, the back surface 21b side of the protective member 21 attached to the workpiece 11 is held by the chuck table. Figure 2 is a cross-sectional view that shows a schematic view of the workpiece 11 being held by the chuck table 4 via the protective member 21. Note that the grinding device 2 shown in Figure 2 etc. is used in each of the following steps.

The grinding device 2 is equipped with a chuck table (first chuck table, second chuck table) 4 configured to hold the workpiece 11. The chuck table 4 includes a disk-shaped frame 6 formed from, for example, ceramics, stainless steel, or the like. A recess 6a having a circular opening at the upper end is formed on the upper surface side of the frame 6. A holding plate 8 formed into a porous disk shape using ceramics or the like is fixed to this recess 6a.

The upper surface 8a of the holding plate 8 is configured, for example, in a shape corresponding to the side surface of a cone, and functions as a holding surface that holds the protective member 21. In this embodiment, the back surface 21b of the protective member 21 is brought into contact with the upper surface (first holding surface, second holding surface) 8a. The lower surface side of the holding plate 8 is connected to a suction source (not shown) such as an ejector via a flow path 6b provided inside the frame 6, a valve (not shown), etc.

Therefore, by contacting the back surface 21b of the protective member 21 with the upper surface 8a of the holding plate 8, opening the valve, and applying negative pressure from the suction source, the back surface 21b of the protective member 21 is sucked by the chuck table 4. In other words, the workpiece 11 is held by the chuck table 4 via the protective member 21 attached to the front surface 11a side.

Then, as shown in Figure 2, the back surface 11b side of the workpiece 11 is exposed upward. Note that in Figure 2 and other figures, the shape of the upper surface 8a of the holding plate 8 is exaggerated, but in reality, the difference in height (height difference) between the apex 8b of the upper surface 8a, which corresponds to the apex of the cone, and the outer periphery of the upper surface 8a is a maximum of about 10 μm to 30 μm.

A rotational drive source (not shown) such as a motor is connected to the bottom of the frame 6. The force generated by this rotational drive source causes the chuck table 4 to rotate around a rotation axis along the vertical direction or a rotation axis slightly tilted relative to the vertical direction, with the apex 8b as the center of rotation. The frame 6 is also supported by a chuck table movement mechanism (not shown), and the force generated by this chuck table movement mechanism causes the chuck table 4 to move horizontally.

After the workpiece 11 is held by the chuck table 4 via the protective member 21, for example, the area of the workpiece 11 corresponding to the area (device area) where the device 15 is formed is roughly ground from the back surface 11b side (first grinding step). Figure 3 is a cross-sectional view showing the state in which the workpiece 11 is roughly ground. Note that in Figure 3, for convenience of explanation, some elements are shown from the side.

As shown in FIG. 3 etc., a first grinding unit (rough grinding unit) 10 is disposed above the chuck table 4 of the grinding device 2. The first grinding unit 10 includes, for example, a cylindrical spindle housing (not shown). A columnar spindle 12 is housed in the space inside the spindle housing.

At the lower end of the spindle 12, for example, a disk-shaped mount 14 having a diameter smaller than the workpiece 11 or the protective member 21 is provided. A plurality of holes (not shown) are formed on the outer periphery of the mount 14, penetrating the mount 14 in the thickness direction, and a bolt 16 or the like is inserted into each hole. A disk-shaped first grinding wheel (coarse grinding wheel) 18 having roughly the same diameter as the mount 14 is fixed to the underside of the mount 14 by the bolt 16 or the like.

The first grinding wheel 18 includes a disk-shaped wheel base 20 made of a metal such as stainless steel or aluminum. A plurality of first grinding stones (coarse grinding stones) 22 are fixed to the underside of the wheel base 20 along the circumferential direction of the wheel base 20. The first grinding stones 22 have a structure in which large abrasive grains made of, for example, diamonds or the like are dispersed in a binder made of resin or the like.

When the first grinding wheel 18 including this first grinding stone 22 is used, the amount of workpiece 11 that can be removed per unit time increases, but a damaged layer containing scratches or distortion is more likely to form on the grinding surface side of the workpiece 11. A rotational drive source such as a motor (not shown) is connected to the upper end side of the spindle 12. The force generated by this rotational drive source causes the first grinding wheel 18 to rotate around a rotational axis that is aligned along the vertical direction or a rotational axis that is slightly tilted relative to the vertical direction.

A nozzle (not shown) configured to supply a grinding liquid (typically water) to the first grinding stone 22 and the like is provided next to or inside the first grinding wheel 18. The spindle housing is supported, for example, by a first grinding unit moving mechanism (not shown), and the first grinding unit 10 moves vertically by the force generated by this first grinding unit moving mechanism.

When grinding the workpiece 11 with the first grinding unit 10 (first grinding wheel 18), for example, the chuck table 4 is moved directly below the first grinding unit 10. Specifically, the chuck table 4 is moved horizontally by the chuck table moving mechanism so that the first grinding wheel 18 (all first grinding wheels 22) are positioned directly above the area where the device 15 is formed.

Also, as shown in FIG. 3, the angle between the rotation axis of the first grinding wheel 18 (first grinding stone 22) and the rotation axis of the chuck table 4 is adjusted so that the distance between the first grinding wheel 18 (first grinding wheel 22) and the chuck table 4 (upper surface 8a of the holding plate 8) is wider on the outer edge side far from the rotation axis of the chuck table 4 than on the center side close to the rotation axis of the chuck table 4. There are no particular limitations on the adjustment method, but it is preferable to adjust, for example, one or both of the inclination of the rotation axis of the chuck table 4 and the inclination of the rotation axis of the first grinding wheel 18.

In this embodiment, the angle between the rotation axis of the first grinding wheel 18 and the rotation axis of the chuck table 4 is adjusted after the chuck table 4 is moved directly below the first grinding unit 10. However, the angle between the rotation axis of the first grinding wheel 18 and the rotation axis of the chuck table 4 may be adjusted before the workpiece 11 is held by the chuck table 4, and then the chuck table 4 may be moved directly below the first grinding unit 10. Of course, the angle between the rotation axis of the first grinding wheel 18 and the rotation axis of the chuck table 4 may be adjusted before the workpiece 11 is held by the chuck table 4.

Then, the chuck table 4 and the first grinding wheel 18 are rotated, and the first grinding unit 10 (first grinding wheel 18) is lowered while liquid is supplied from the nozzle. In other words, the first grinding wheel 18 and the chuck table 4 are moved relatively in a direction intersecting with the upper surface 8a, and the workpiece 11 is ground by the first grinding wheel 18. The speed at which the first grinding unit 10 is lowered (grinding feed rate) is adjusted to a range in which the first grinding wheel 22 is pressed against the workpiece 11 with an appropriate pressure.

Figure 4 is a cross-sectional view showing a schematic of a portion of the workpiece 11 after being ground by the first grinding wheel 18. As described above, by grinding the area of the workpiece 11 corresponding to the area where the device 15 is formed from the back surface 11b side, as shown in Figure 4, it is possible to form a disk-shaped first thin plate portion 11c corresponding to the area where the device 15 is formed, and an annular first thick plate portion 11d surrounding the first thin plate portion 11c, on the workpiece 11.

In this embodiment, as described above, the workpiece 11 is ground with the angle between the rotation axis of the first grinding wheel 18 and the rotation axis of the chuck table 4 adjusted so that the distance between the first grinding wheel 18 equipped with the first grinding stone 22 containing abrasive grains and the upper surface 8a of the chuck table 4 is wider on the outer edge side far from the rotation axis of the chuck table 4 than on the central side closer to the rotation axis of the chuck table 4. Therefore, the outer edge side of the first thin plate portion 11c is thicker than the central side.

In addition, a damaged layer 11e containing scratches or distortion is formed on the portion (ground surface) of the first thin plate portion 11c on the back surface 11b side. Therefore, it is desirable that at least the outer edge side of the first thin plate portion 11c remaining on the workpiece 11 is formed to a thickness that prevents cracks from reaching the device 15 on the front surface 11a side even if cracks extend from the damaged layer 11e during subsequent transportation, etc. For example, when the workpiece 11 is a silicon wafer, by forming the outer edge side of the first thin plate portion 11c to a thickness of 150 μm or more, preferably 200 μm or more, cracks extending from the damaged layer 11e will not substantially reach the device 15.

There are no significant limitations to the specific grinding conditions. To achieve efficient grinding of the workpiece 11, the rotation speed of the chuck table 4 should be set to 100 rpm to 600 rpm, typically 300 rpm, and the rotation speed of the first grinding wheel 18 should be set to 1000 rpm to 7000 rpm, typically 4500 rpm.

The speed of descent of the first grinding unit 10 (first grinding wheel 18) may be set to 0.8 μm/s to 10 μm/s. Furthermore, the speed of descent of the first grinding unit 10 may be changed in accordance with the progress of grinding. Typically, three speed stages of 6.0 μm/s, 3.0 μm/s, and 1.0 μm/s are set in sequence in accordance with the progress of grinding.

After grinding the workpiece 11 from the back surface 11b side to form the disk-shaped first thin plate portion 11c and the annular first thick plate portion 11d surrounding the first thin plate portion 11c, the first thin plate portion 11c is ground with higher precision from the back surface 11b side (second grinding step). Figure 5 is a cross-sectional view showing the workpiece 11 being ground with high precision. Note that in Figure 5, for ease of explanation, some elements are shown from the side.

As shown in FIG. 5, a second grinding unit (finish grinding unit) 24, which is separate from the first grinding unit 10, is disposed above the chuck table 4 of the grinding device 2. The second grinding unit 24 includes, for example, a cylindrical spindle housing (not shown). A columnar spindle 26 is housed in the space inside the spindle housing.

At the lower end of the spindle 26, for example, a disk-shaped mount 28 having a diameter smaller than the workpiece 11 or the protective member 21 is provided. A plurality of holes (not shown) are formed on the outer periphery of the mount 28, penetrating the mount 28 in the thickness direction, and a bolt 30 or the like is inserted into each hole. A disk-shaped second grinding wheel (finish grinding wheel) 32 having roughly the same diameter as the mount 28 is fixed to the underside of the mount 28 by the bolt 30 or the like.

The second grinding wheel 32 includes a disk-shaped wheel base 34 made of a metal such as stainless steel or aluminum. A plurality of second grinding wheels (finishing grinding wheels) 36 are fixed to the underside of the wheel base 34 along the circumferential direction of the wheel base 34. The second grinding wheel 36 has a structure in which smaller abrasive grains made of, for example, diamonds are dispersed in a binder made of resin or the like. Specifically, the size of the abrasive grains contained in the second grinding wheel 36 (typically, the average grain size) is smaller than the size of the abrasive grains contained in the first grinding wheel 22.

When the second grinding wheel 32 including this second grinding stone 36 is used, the amount of workpiece 11 that can be removed per unit time is reduced, while a damaged layer containing scratches or distortion is less likely to form on the grinding surface side of the workpiece 11. A rotational drive source such as a motor (not shown) is connected to the upper end side of the spindle 26. The second grinding wheel 32 rotates around a rotational axis along the vertical direction or a rotational axis slightly tilted from the vertical direction by the force generated by this rotational drive source.

A nozzle (not shown) configured to supply a grinding liquid (typically water) to the second grinding wheel 36 and the like is provided next to or inside the second grinding wheel 32. The spindle housing is supported, for example, by a second grinding unit movement mechanism (not shown), and the second grinding unit 24 moves vertically by the force generated by this second grinding unit movement mechanism.

When grinding the first thin plate portion 11c with the second grinding unit 24 (second grinding wheel 32), first, the chuck table 4 is moved directly below the second grinding unit 24. Specifically, the chuck table 4 is moved horizontally by the chuck table moving mechanism so that the second grinding wheel 32 (all second grinding wheels 36) are positioned directly above the first thin plate portion 11c.

Also, as shown in FIG. 5, the angle between the rotation axis of the second grinding wheel 32 and the rotation axis of the chuck table 4 is adjusted so that the difference between the distance between the second grinding wheel 32 (second grinding wheel 36) and the chuck table 4 (upper surface 8a of the holding plate 8) at the center near the rotation axis of the chuck table 4 and the distance at the outer edge far from the rotation axis of the chuck table 4 is smaller than the difference between the distance between the first grinding wheel 18 (first grinding wheel 22) and the chuck table 4 (upper surface 8a of the holding plate 8) at the center near the rotation axis of the chuck table 4 and the distance at the outer edge far from the rotation axis of the chuck table 4 during the rough grinding described above.

In this embodiment, as shown in FIG. 5, the angle between the rotation axis of the second grinding wheel 32 (second grinding wheel 36) and the chuck table 4 (upper surface 8a of the holding plate 8) is adjusted so that the difference between the distance between the center side close to the rotation axis of the chuck table 4 and the distance between the center side far from the rotation axis of the chuck table 4 is sufficiently small (substantially zero). There are no particular limitations on the adjustment method, but it is preferable to adjust, for example, one or both of the inclination of the rotation axis of the chuck table 4 and the inclination of the rotation axis of the second grinding wheel 32.

In this embodiment, the angle between the rotation axis of the second grinding wheel 32 and the rotation axis of the chuck table 4 is adjusted after the chuck table 4 is moved directly below the second grinding unit 24. However, the angle between the rotation axis of the second grinding wheel 32 and the rotation axis of the chuck table 4 may be adjusted before the workpiece 11 is held by the chuck table 4.

Then, the chuck table 4 and the second grinding wheel 32 are rotated, and the second grinding unit 24 (second grinding wheel 32) is lowered while liquid is supplied from the nozzle. In other words, the second grinding wheel 32 and the chuck table 4 are moved relative to each other in a direction intersecting with the upper surface 8a. The speed at which the second grinding unit 24 is lowered (grinding feed rate) is adjusted to a range in which the second grinding wheel 36 is pressed against the workpiece 11 with an appropriate pressure.

Figure 6 is a cross-sectional view showing a schematic of a portion of the workpiece 11 after the first thin plate portion 11c has been ground by the second grinding wheel 32. As described above, by grinding the first thin plate portion 11c from the back surface 11b side, as shown in Figure 6, a second thin plate portion 11f that is a disk-shaped portion having a smaller diameter and thinner than the first thin plate portion 11c, and a second thick plate portion 11g that is annular and surrounds the second thin plate portion 11f can be formed in the first thin plate portion 11c.

In this embodiment, as described above, the first thin plate portion 11c is ground in a state in which the angle between the rotation axis of the second grinding wheel 32 and the rotation axis of the chuck table 4 is adjusted so that the difference between the distance between the second grinding wheel 32 equipped with the second grinding wheel 36 containing smaller abrasive grains than the first grinding wheel 22 and the upper surface 8a of the chuck table 4 at the center side close to the rotation axis of the chuck table 4 and the distance at the outer edge side far from the rotation axis of the chuck table 4 is smaller than the difference between the distance between the first grinding wheel 18 and the upper surface 8a of the chuck table 4 at the center side close to the rotation axis of the chuck table 4 and the distance at the outer edge side far from the rotation axis of the chuck table 4 during rough grinding. Therefore, the second thin plate portion 11f having a smaller difference in thickness between the outer edge side and the center side compared to the first thin plate portion 11c can be formed while removing the damaged layer 11e including scratches or distortion formed in the first thin plate portion 11c.

There are no significant limitations to the specific grinding conditions. To achieve efficient and highly accurate grinding of the workpiece 11, the rotation speed of the chuck table 4 should be set to 100 rpm to 600 rpm, typically 300 rpm, and the rotation speed of the second grinding wheel 32 should be set to 1000 rpm to 7000 rpm, typically 4000 rpm.

In addition, since the grinding with the second grinding wheel 32 grinds the first thin plate portion 11c, which is thinner at the center than at the outer edge, the volume of the workpiece 11 removed by the second grinding wheel 32 is smaller than when the first thin plate portion, which is thick overall, is processed into the second thin plate portion. Therefore, for example, when grinding the outer edge side of the first thin plate portion 11c, it is possible to increase the speed of descent of the second grinding unit 24 compared to when grinding the first thin plate portion, which is thick overall.

For example, in this embodiment, the speed of descent of the second grinding unit 24 when grinding the outer edge side of the first thin plate portion 11c is set to 0.8 μm/s to 5.0 μm/s, and the speed of descent of the second grinding unit 24 when grinding both the outer edge side and the center side of the first thin plate portion 11c is set to 0.1 μm/s to 0.8 μm/s.

That is, the speed of descent of the second grinding unit 24 at the stage of grinding the outer edge side of the first thin plate portion 11c is set to be greater than the speed of descent of the second grinding unit 24 at the stage of grinding both the outer edge side and the center side of the first thin plate portion 11c. Typically, four speed stages of 1.5 μm/s, 1.3 μm/s, 0.6 μm/s, and 0.3 μm/s are set in sequence according to the progress of grinding. This makes it possible to sufficiently reduce the amount of scratches and distortions formed in the second thin plate portion 11f while shortening the time required for grinding and increasing efficiency. In other words, the generation of a new damaged layer can be prevented without significantly increasing the time required to complete grinding.

Although the damaged layer 11e remains in the second thick plate portion 11g (the outer edge side of the first thin plate portion 11c) that is not ground by the second grinding wheel 32, the distance from this damaged layer 11e to the device 15 on the front surface 11a side is sufficiently large. Therefore, during subsequent transportation, etc., the probability that a crack will extend from the remaining damaged layer 11e to the device 15 on the front surface 11a side is also sufficiently low.

In order to prevent the above-mentioned damaged layer 11e from remaining in the second thin plate portion 11f of the workpiece 11, it is necessary to thoroughly grind the workpiece 11 (first thin plate portion 11c) using this second grinding wheel 32 (second grinding stone 36). Specifically, if the thickness to be removed by the second grinding wheel 32 to completely remove the damaged layer 11e is A or more, the thickness to be removed at the thinnest central portion of the first thin plate portion 11c will be A or more.

Therefore, if the distance by which the second grinding wheel 32 is lowered during grinding (the thickness removed by grinding using the second grinding wheel 32) is B, in order to prevent the damaged layer 11e from remaining in the second thin plate portion 11f, it is necessary to keep the height difference between the outer edge and center of the first thin plate portion 11c to less than (B - A). For example, if the grinding thickness A required to completely remove the damaged layer 11e is 30 μm and the distance B by which the second grinding wheel 32 is lowered is 100 μm, then the upper limit of the height difference (B - A) is 70 μm.

There is no significant lower limit to the height difference between the outer edge and center of the first thin plate portion 11c, but if this height difference becomes too small, it becomes difficult to increase the speed of descent of the second grinding unit 24, and the effectiveness of the grinding method for the workpiece according to this embodiment decreases. Therefore, it is desirable for the lower limit of the height difference to be approximately (B - A - 30 μm).

In other words, in the above-mentioned rough grinding (first grinding step), it is desirable to adjust the angle between the rotation axis of the chuck table 4 and the rotation axis of the first grinding wheel 18 so that the height difference between the outer edge side and the center side of the first thin plate portion 11c to be formed is (B-A-30 μm) to (B-A).

Next, examples and comparative examples conducted to confirm the effect of the grinding method for a workpiece according to this embodiment will be described. In the examples and comparative examples, the grinding time required to grind a workpiece having a thickness of approximately 725 μm to obtain a second thin plate portion having a thickness of approximately 100 μm was confirmed. In the examples, the workpiece 11 was first ground using the first grinding wheel 18 to form a first thin plate portion 11c having a thickness of 200 μm and a first thick plate portion 11d having a thickness of 725 μm.

The speed at which the first grinding wheel 18 was lowered when grinding the workpiece 11 (grinding feed rate) was set to 6.0 μm/s, 3.0 μm/s, and 1.0 μm/s in that order according to the progress of grinding. The distance by which the first grinding wheel 18 was lowered at each speed (i.e., the thickness removed by grinding) was 465 μm at a speed of 6.0 μm/s, 30 μm at a speed of 3.0 μm/s, and 30 μm at a speed of 1.0 μm/s. The angle between the rotation axis of the chuck table 4 and the rotation axis of the first grinding wheel 18 was adjusted so that the height difference between the outer edge side and the center side of the first thin plate portion 11c was approximately 70 μm.

Then, the first thin plate portion 11c was ground using the second grinding wheel 32 to form a second thin plate portion 11f having a thickness of about 100 μm. The speed at which the second grinding wheel 32 was lowered when grinding the first thin plate portion 11c (grinding feed rate) was set to 1.5 μm/s, 1.3 μm/s, 0.6 μm/s, and 0.3 μm/s in that order according to the progress of grinding. The distance at which the second grinding wheel 32 was lowered at each speed was 30 μm at a speed of 1.5 μm/s, 30 μm at a speed of 1.3 μm/s, 30 μm at a speed of 0.6 μm/s, and 10 μm at a speed of 0.3 μm/s. The angle between the rotation axis of the chuck table 4 and the rotation axis of the second grinding wheel 32 was adjusted so that the difference in height between the outer edge side and the center side of the second thin plate portion 11f was essentially zero. In this example, the total grinding time was approximately 244 seconds.

In the comparative example, the workpiece was ground using the first grinding wheel 18 to form a first thin plate portion having a thickness of 200 μm and a first thick plate portion having a thickness of 725 μm. The speed at which the first grinding wheel 18 was lowered when grinding the workpiece (grinding feed rate) was set to 6.0 μm/s, 3.0 μm/s, and 1.0 μm/s in that order according to the progress of grinding. The distance at which the first grinding wheel 18 was lowered at each speed was 465 μm at a speed of 6.0 μm/s, 30 μm at a speed of 3.0 μm/s, and 30 μm at a speed of 1.0 μm/s. However, the angle between the rotation axis of the chuck table 4 and the rotation axis of the first grinding wheel 18 was adjusted so that the height difference between the outer edge side and the center side of the first thin plate portion was substantially zero.

Then, the first thin plate portion was ground using the second grinding wheel 32 to form a second thin plate portion having a thickness of about 100 μm. The speed at which the second grinding wheel 32 was lowered when grinding the first thin plate portion (grinding feed rate) was set to 0.6 μm/s and 0.3 μm/s in that order according to the progress of grinding. The distance at which the second grinding wheel 32 was lowered at each speed was 90 μm at a speed of 0.6 μm/s and 10 μm at a speed of 0.3 μm/s. The angle between the rotation axis of the chuck table 4 and the rotation axis of the second grinding wheel 32 was adjusted so that the difference in height between the outer edge side and the center side of the second thin plate portion was substantially zero. In the comparative example, the total grinding time was about 301 s. In other words, in the example, the total grinding time was about 57 s shorter than in the comparative example.

As described above, in the grinding method of the workpiece according to the present embodiment, the angle between the rotation axis of the first grinding wheel 18 and the rotation axis of the chuck table (first chuck table) 4 is adjusted so that the distance between the first grinding wheel 18 equipped with the first grinding stone 22 containing abrasive grains and the upper surface (first holding surface) 8a of the holding plate 8 of the chuck table (first chuck table) 4 is wider on the outer edge side far from the rotation axis of the chuck table (first chuck table) 4 than on the center side close to the rotation axis of the chuck table (first chuck table) 4. The workpiece 11 is ground to form a disk-shaped first thin plate portion 11c and an annular first thick plate portion 11d surrounding the first thin plate portion 11c, so that the outer edge side of the first thin plate portion 11c is thicker than the center side.

Then, the difference between the distance between the second grinding wheel 32 equipped with the second grinding wheel 36 containing smaller abrasive grains than the first grinding wheel 22 and the upper surface (second holding surface) 8a of the holding plate 8 of the chuck table (second chuck table) 4 at the center side close to the rotation axis of the chuck table (second chuck table) 4 and the distance at the outer edge side far from the rotation axis of the chuck table (second chuck table) 4 is the difference between the distance between the first grinding wheel 18 and the upper surface (first holding surface) 8a of the holding plate 8 of the chuck table (first chuck table) 4 at the center side close to the rotation axis of the chuck table (first chuck table) 4 and the distance at the outer edge side far from the rotation axis of the chuck table (second chuck table) 4. The first thin plate portion 11c is ground in a state in which the angle between the rotation axis of the second grinding wheel 32 and the rotation axis of the chuck table (second chuck table) 4 is adjusted so that the difference between the distance from the outer edge side far from the rotation axis of the (first chuck table) 4 and the distance from the outer edge side to the center side is smaller than the difference between the distance from the outer edge side to the center side. A second thin plate portion 11f that is a disk-shaped plate and has a smaller diameter than the first thin plate portion 11c and a second thick plate portion 11g that is annular and surrounds the second thin plate portion 11f are formed in the first thin plate portion 11c. This makes it possible to form a second thin plate portion 11f that has a smaller difference in thickness between the outer edge side and the center side than the first thin plate portion 11c while removing a damaged layer 11e that includes scratches or distortion formed in the first thin plate portion 11c.

In addition, in the grinding method of the workpiece according to this embodiment, the outer edge side of the first thin plate portion 11c that remains in the workpiece 11 as the second thick plate portion 11g is thicker than the center side of the first thin plate portion 11c, and the distance from the damage layer 11e formed in the second thick plate portion 11g (i.e., the outer edge side of the first thin plate portion 11c) to the surface 11a of the workpiece 11 is sufficiently large, so that during subsequent transportation, etc., the possibility of a crack extending from the damage layer 11e of the second thick plate portion 11g to the surface 11a of the workpiece 11 and damaging the device 15 is reduced.

Furthermore, in the grinding method of the workpiece according to this embodiment, the first thin plate portion 11c is formed so that the center side is thinner than the outer edge side, and therefore the volume of the workpiece 11 removed by the second grinding wheel 32 is smaller than when the first thin plate portion, which is thick overall, is processed into the second thin plate portion. Therefore, even if the distance from the device 15 to the damaged layer 11e of the second thick plate portion 11g (the outer edge side of the first thin plate portion 11c) is made sufficiently large, the time until grinding is completed is not significantly extended. Thus, according to the grinding method of the workpiece according to this embodiment, the probability of damage to the device 15 can be reduced without significantly extending the time until grinding is completed.

The present invention is not limited to the above-described embodiment, and can be modified in various ways. For example, in the above-described embodiment, the workpiece 11 held by the chuck table 4 is ground by the first grinding wheel 18, and then the workpiece 11 held by the same chuck table 4 is ground by the second grinding wheel 32. In other words, the first chuck table used when grinding the workpiece 11 by the first grinding wheel 18 is used as the second chuck table when grinding the workpiece 11 by the second grinding wheel 32.

In contrast to this, the workpiece 11 held by the chuck table 4 can be ground by the first grinding wheel 18, and then the workpiece 11 held by a chuck table other than the chuck table 4 can be ground by the second grinding wheel 32. In other words, the first chuck table used when grinding the workpiece 11 by the first grinding wheel 18 and the second chuck table used when grinding the workpiece 11 by the second grinding wheel 32 can be different. Similarly, the grinding method of the workpiece according to the present invention can be performed using multiple grinding devices.

In addition, the structures, methods, etc. of the above-mentioned embodiments and variations can be modified as appropriate without departing from the scope of the present invention.

11: Workpiece 11a: Front surface 11b: Back surface 11c: First thin plate portion 11d: First thick plate portion 11e: Damaged layer 11f: Second thin plate portion 11g: Second thick plate portion 13: Planned division line (street)
15: Device 21: Protective member 21a: Front surface 21b: Back surface 2: Grinding device 4: Chuck table (first chuck table, second chuck table)
6: Frame 6a: Recess 6b: Flow path 8: Holding plate 8a: Upper surface (first holding surface, second holding surface)
8b: Apex 10: First grinding unit (rough grinding unit)
12: Spindle 14: Mount 16: Bolt 18: First grinding wheel (rough grinding wheel)
20: Wheel base 22: First grinding wheel (rough grinding wheel)
24: Second grinding unit (finish grinding unit)
26: Spindle 28: Mount 30: Bolt 32: Second grinding wheel (finish grinding wheel)
34: Wheel base 36: Second grinding wheel (finishing grinding wheel)

Claims (3)

A method for grinding a workpiece, comprising the steps of: grinding a plate-shaped workpiece having a plurality of devices provided on a front surface side from a back surface side opposite to the front surface using a grinding wheel attached to a rotating spindle, the method comprising the steps of:
a step of attaching a protective member to the surface of the workpiece;
a first grinding step in which the workpiece is held on a first holding surface of a first chuck table via the protective member, and an angle between a rotation axis of the first grinding wheel and a rotation axis of the first chuck table is adjusted so that a distance between a first grinding wheel equipped with a first grinding stone containing abrasive grains and the first holding surface is wider on an outer edge side far from the rotation axis of the first chuck table than on a central side close to the rotation axis of the first chuck table, while rotating the first grinding wheel and the first chuck table, thereby grinding the workpiece from the back surface side and forming a disk-shaped first thin plate portion and an annular first thick plate portion surrounding the first thin plate portion in the workpiece;
After the first grinding step, the workpiece is held on a second holding surface of a second chuck table via the protective member, and a difference between a distance between a second grinding wheel provided with a second grinding wheel containing smaller abrasive grains than the first grinding wheel and the second holding surface at a center side close to the rotation axis of the second chuck table and a distance between an outer edge side far from the rotation axis of the second chuck table is a difference between a distance between the first grinding wheel and the first holding surface at a center side close to the rotation axis of the first chuck table and a distance between an outer edge side far from the rotation axis of the first chuck table. and a second grinding step of rotating the second grinding wheel and the second chuck table while relatively moving the second grinding wheel and the second chuck table in a direction intersecting the second holding surface to grind the first thin plate portion from the back surface side, while adjusting an angle between the rotation axis of the second grinding wheel and the rotation axis of the second chuck table so that the angle is smaller than the difference between the first and second thin plate portions, thereby forming, in the first thin plate portion, a second thin plate portion that is circular and thinner and has a smaller diameter than the first thin plate portion, and a second thick plate portion that is annular and surrounds the second thin plate portion. The method for grinding a workpiece according to claim 1, wherein the first chuck table is used as the second chuck table. The method for grinding a workpiece according to claim 1 or 2, wherein in the first grinding step, the first thin plate portion is formed to a thickness such that cracks extending from a damaged layer including scratches or distortions generated on the outer edge side of the first thin plate portion in the first grinding step do not reach the device.

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